The present invention relates to a tire with radial carcass reinforcement, and more particularly to a xe2x80x9cheavy-vehiclexe2x80x9d-type tire, intended to be fitted on a vehicle, such as a lorry, road tractor, bus, trailer and others. More specifically, it relates to a novel bead structure.
Generally, a tire of the type in question comprises a carcass reinforcement formed of at least one ply of metal cables, which is anchored in each bead to at least one bead wire, forming an upturn. The carcass reinforcement is radially surmounted by a crown reinforcement, composed of at least two plies of metal cables, crossed from one ply to the next and forming angles of between 10xc2x0 and 45xc2x0 with the circumferential direction. The carcass reinforcement upturns are generally reinforced by at least one ply of metal cables oriented at a small angle relative to the circumferential direction.
In the case of the tire in question, the reinforcement ply of the bead may be wound around the bead wire, so as to have an axially outer strand and an axially inner strand, the radially upper end of the axially inner strand being generally located beneath the radially upper end of the axially outer strand.
The known solution aims to avoid deradialization of the cables of the upturn of the carcass reinforcement, and to minimize the radial and circumferential deformations to which the end of said upturn, and the outer layer of rubber covering the bead and effecting the connection to the rim are subjected.
French Application FR 98/09451 of Jul. 23, 1998, in order to improve the endurance of a tire having beads intended to be mounted on rim seats which are flat or are inclined at 5xc2x0, uses a bead reinforcement armature having radial elements. The tire described in said application has each bead provided with a first reinforcement armature formed of at least one ply of radial reinforcement elements which is wound around the anchoring bead wire of the carcass reinforcement and on the inside of said carcass reinforcement to form two strands such that the axially inner strand, between its radially upper edge parallel to the meridian profile of the carcass reinforcement and its point of tangency to the anchoring bead wire, follows a rectilinear trace referred to as xe2x80x9cshortest-pathxe2x80x9d and that the radially upper end of said axially inner strand is radially located at a distance HLI from the base of the bead of between 80% and 160% of the distance HRNC, the radial distance between the end of the carcass reinforcement upturn and the base of the bead, the second armature of elements inclined relative to the radial direction not being wound around said anchoring bead wire and arranged axially to the outside of the carcass reinforcement upturn.
The radial reinforcement elements of the ply or plies of the bead reinforcement armature are preferably inextensible metallic elements, made of steel and in the form of cables.
The French application referred to above furthermore proposes, in order to improve the resistance of the carcass reinforcement to rupture of reinforcement elements occurring in its portions which form an integral part of the beads, to impart to said portions the same profile as that of the bead reinforcement plies having radial elements, that is to say, a rectilinear profile.
Research has shown that such a bead reinforcement structure with, in particular, a rectilinear meridian profile of the main part of the carcass reinforcement which is at a tangent to the anchoring bead wire could be substantially improved by a judicious selection of the vulcanized rubber mixes forming the bead of the tire.
The tire according to the invention, having a radial carcass reinforcement, anchored in each bead to an anchoring bead wire to form an upturn, the anchoring bead wire being surmounted radially by a first profiled member of vulcanized rubber mix and of a substantially triangular shape when viewed in meridian section, the upper edge of the upturn being separated from the main part of said reinforcement by a second profiled member of vulcanized rubber mix, is characterized in that the secant modulus of elasticity in tension of the first profiled member, measured for a relative elongation of 10%, is between 8 and 10 MPa, whereas the secant modulus of elasticity in tension of the second profiled member, measured under the same conditions, is between 3 and 5 MPa, a third profiled member of vulcanized rubber mix being arranged axially to the outside of the carcass reinforcement upturn and the secant modulus of elasticity in tension of which, measured under the same conditions, is between 35 and 50 MPa, whereas a fourth profiled member radially surmounting the third profiled member has a secant modulus of elasticity in tension, measured under the same conditions, of between 3 and 5 MPa, the radially lower end of said fourth profiled member being located radially at a distance less than the distance between the end of the upturn of the carcass reinforcement and the base D of the beads, the third profiled member having a thickness which decreases radially towards the outside, such that the radial distance separating the straight line D from the point of the straight line parallel to the axis of rotation for which said thickness is equal to 10% of the maximum thickness is less than the radial distance between the end of the carcass reinforcement upturn and said straight line D, and said main part of the carcass reinforcement having a substantially rectilinear meridian profile between its point of tangency T to the anchoring bead wire and a point A located at a distance HA from the base D of between 35% and 65% of the radial distance HE between the points of maximum axial width of said carcass reinforcement and said base D.
The presence of a third profiled member of very high modulus of elasticity and included axially between the carcass reinforcement upturn and the layer of rubber mix which effects the contact with the rim flange and the secant modulus of elasticity in tension of which is between 10 and 15 MPa, avoids virtually any rotational movement of the anchoring bead wire of the carcass reinforcement, whatever the structure of said bead wire, the effect obtained however being significantly greater for a bead wire of the xe2x80x9cbraidedxe2x80x9d type.
It is particularly advantageous for the third profiled member to be extended, radially to the inside, so as to be able to be turned up about the bead wire assembly and thus to cover at least half a circumference of the above assembly. xe2x80x9cBead wire assemblyxe2x80x9d as used herein means an assembly formed mainly of the bead wire, the carcass reinforcement and possibly one or more additional reinforcement armatures.
The anchoring bead wire of the carcass reinforcement is generally surrounded by a layer of vulcanized mix: the secant modulus of elasticity in tension of said layer which surrounds the anchoring bead wire will be substantially equal to the secant modulus of elasticity in tension of the third profiled member.
The life of the bead comprising such profiled members will be improved by the addition, between the main part of the carcass reinforcement and the carcass reinforcement upturn, of a reinforcement armature formed of a ply of radial reinforcement elements which is wound around the anchoring bead wire to form two strands, the radially upper end of the axially inner strand being radially located at a distance HLI from the base of the bead of between 80% and 160% of the distance HRNC, the radial distance between the end of the carcass reinforcement upturn and the base of the bead, located axially to the inside of the upturn of the carcass reinforcement, preferably having its radially upper end radially closer to the axis of rotation than the end of the carcass reinforcement upturn, the distance HLE between said end and the base of the bead being between 0.2 and 0.8 times the height HRNC of the carcass reinforcement upturn.